The present invention relates to carbon-containing refractories and, in particular, magnesite-carbon refractory brick suitable for use in metal processing equipment, especially basic oxygen furnaces (BOF) and other metallurgical vessels wherein the principal mode of wear of the refractory brick lining is slag attack and where hot strength and high slag resistance of refractory linings are required. Furthermore, this invention is applicable to unburned alumina-carbon refractories such as those used in slide gates and shroud tubes which control the flow of molten steel in the continuous casting process in which properties comparable to shapes containing B.sub.4 C are desired.
There is abundant prior art dealing with the use of metals in carbon-containing refractories. Essentially, the purpose of these metals is to act as oxygen "getters" which combine with free oxygen before the oxygen can consume carbon in the refractory. Another purpose of the powdered metals is to form, under certain conditions, stable carbide phases which decrease the permeability of the refractory and increase its strength. U.S. Pat. No. 4,306,030 discloses the use of aluminum, silicon, and magnesium metal powders. These metals increase the oxidation resistance of the refractory and have the effect of lowering the permeability of the brick which makes the entrance of oxidizing gases into the refractory more difficult. It is also known that these metals can be effective if used individually or in combination or as alloys in various combinations.
Prior art also discloses the use of various carbides and nitrides either used individually or in combination with the three primary metals, silicon, aluminum, or magnesium. The purpose of these carbides (such as B.sub.4 C or SiC) or nitrides (such as BN or Si.sub.3 N.sub.4) is to increase the hot strength or corrosion resistance. U.S. Pat. No. 4,471,059, for example, teaches the addition of 0.3 to 5% B.sub.4 C to a carbon-containing refractory which contains metal additions such as Al, Si, Cr, or Ni. U.S. Pat. No. 4,540,675 teaches the use of 1-10 wt. % B.sub.4 C as an anti-oxidant. B.sub.4 C is effective because it has a relatively high affinity for oxygen and oxidizes to an oxide. This oxide then in turn reacts with magnesia, silica or a silicate to produce a viscous glass film in the refractory which further decreases the permeability of the refractory. U.S. Pat. No. 4,605,635 shows the use in carbon-containing refractories of SiB.sub.6. The boron portion oxidizes to B.sub.2 O.sub.3, which then reacts with magnesia, the silicon portion which also oxidizes to a silicate and reacts with magnesium borate to form a lower melting liquid. While the carbonaceous material is better protected against oxidation, the presence of the silicate results in low and undesirable hot strengths due to reaction thereof with lime or calcium silicate impurities in the refractory resulting in very low melting fluid lime-magnesia-borosilicates. This low strength causes the refractories to be prone to accelerated wear.